I'm guessing the largest cause of the performance not being great is the large amount of data, and the approach to render it is not optimal. If the same rendering algorithm was implemented using OpenGL instead, I suspect the performance would not be significantly different from this WebGL version.

If you want a random example of a well-optimized demo that uses WebGL for rendering, try the demo at https://www.funkykarts.rocks/demo.html and see how well that performs.